1. Field of the Invention (Technical Field)
The present invention is a method and apparatus for mass production of individualized reflection holograms and volume diffraction grating devices. The holograms preferably have the capability to be sequentially or individually numbered or otherwise customized with a variety of symbols, for example for security purposes.
2. Background Art
Note that the following discussion refers to a number of publications and references. Discussion of such publications herein is given for more complete background of the scientific principles and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Previous work in reproduction of reflection or volume holograms has primarily been directed toward single units or the copying of an original reflection or volume hologram using traditional holographic copying methods.
Only transmission (2D/3D) and dot matrix holograms have previously been mass produced for the decorative and security markets. An Embossing Master hologram is typically used, which has the disadvantage of being only to replicate the single image of the Embossing Master; there is no provision for sequential numbering or individually controlled image areas. For example, U.S. Pat. Nos. 5,262,879, 5,822,092, and 6,486,982 disclose embossing systems which produce diffraction gratings in a pixilated format.
Vibration has been the primary limitation for the reproduction of reflection holograms in a production environment. A vibration difference between the object recording beam and the reference beam prohibits the formation of a hologram. Dinisyuk-type holograms are less sensitive to this problem. Dinisyuk-type single-beam reflection holograms are well known; typically a single laser beam is transmitted through a photosensitive coated material, for example a film or plate, illuminates an object which is behind the plane of the material and possibly touching the material, and reflects back through the material, forming a volume hologram in the material. Unlike split-beam holographic methods, Dinisyuk holograms have the advantage of being less sensitive to vibration when the object is touching the material. However, there is no existing method capable of mass reproducing such holograms, or providing sequential numbers on successive reproductions thereof.